Bottom Line:
Diesel exhaust has been classified as a potential carcinogen and is associated with various health effects.A previous study showed that the doses for manifesting the mutagenetic effects of diesel exhaust could be reduced when coexposed with ultraviolet-A (UVA) in a cellular system.Our results demonstrated that though coexposure of wild type worms at young adult stage to low doses of DPE (20 μg/mL) plus UVA (0.2, 0.5, and 1.0 J/cm2) did not affect worm development (mitotic germ cells and brood size), it resulted in a significant induction of germ cell death.

ABSTRACTDiesel exhaust has been classified as a potential carcinogen and is associated with various health effects. A previous study showed that the doses for manifesting the mutagenetic effects of diesel exhaust could be reduced when coexposed with ultraviolet-A (UVA) in a cellular system. However, the mechanisms underlying synergistic effects remain to be clarified, especially in an in vivo system. In the present study, using Caenorhabditis elegans (C. elegans) as an in vivo system we studied the synergistic effects of diesel particulate extract (DPE) plus UVA, and the underlying mechanisms were dissected genetically using related mutants. Our results demonstrated that though coexposure of wild type worms at young adult stage to low doses of DPE (20 μg/mL) plus UVA (0.2, 0.5, and 1.0 J/cm2) did not affect worm development (mitotic germ cells and brood size), it resulted in a significant induction of germ cell death. Using the strain of hus-1::gfp, distinct foci of HUS-1::GFP was observed in proliferating germ cells, indicating the DNA damage after worms were treated with DPE plus UVA. Moreover, the induction of germ cell death by DPE plus UVA was alleviated in single-gene loss-of-function mutations of core apoptotic, checkpoint HUS-1, CEP-1/p53, and MAPK dependent signaling pathways. Using a reactive oxygen species (ROS) probe, it was found that the production of ROS in worms coexposed to DPE plus UVA increased in a time-dependent manner. In addition, employing a singlet oxygen (1O2) trapping probe, 2,2,6,6-tetramethyl-4-piperidone, coupled with electron spin resonance analysis, we demonstrated the increased 1O2 production in worms coexposed to DPE plus UVA. These results indicated that UVA could enhance the apoptotic induction of DPE at low doses through a DNA damage-triggered pathway and that the production of ROS, especially (1)O2, played a pivotal role in initiating the synergistic process.

fig5: Effectsof DPE plus UVA on the worms’ development. (A) Age-synchronizedyoung hermaphrodites were treated with either DPE (20 μg/mL)or UVA (0.2–1.0 J/cm2) alone or in combination (DPE+ UVA) for 24 h at 20 °C, then the brood size was counted. (B)The body sizes were determined by measuring the flat surface areaof the worms using ImageJ software, and there was no difference amongall treatments after L1-stage larvae were treated with DPE and/orUVA for 72 h. (C) Life span curves of worms and (D) the percentageof adult worms were scored after L1-stage larvae were treated withDPE and/or UVA for 72 h. Data were pooled from three independent experiments.All values are presented as the means ± SE; n ≥ 20, and * represents P < 0.05.

Mentions:
Environmental stresses could modify the developmentalprocesses when the larvae were exposed to toxicants either in embryonicdevelopment or early developmental stages.39 In C. elegans, germ cell apoptosis commences inearly adulthood and increases over time.24 To exclude the changes of background value, we investigated thedevelopmental effects by DPE plus UVA at different stages. As shownin Figure 2B and Figure 5A, worms coexposed to DPE plus UVA at the L4 stage had little effecton the index of mitotic germ cells and brood size. In addition, thebody size and the life span of worms exposed to DPE plus UVA at theL1 stage were not changed obviously as well (Figure 5B and C). However, there was a slight decrease in the percentageof adult worms compared to that in the single treatment of DPE orUVA, or to the control (in all cases, P > 0.05)whenworms were coexposed to DPE plus UVA at the L1 stage (Figure 5D). The results indicated that the enhanced levelsof germ cell apoptosis after coexposure to DPE plus UVA at the latestage did not result from the modification of the developmental procedure.

fig5: Effectsof DPE plus UVA on the worms’ development. (A) Age-synchronizedyoung hermaphrodites were treated with either DPE (20 μg/mL)or UVA (0.2–1.0 J/cm2) alone or in combination (DPE+ UVA) for 24 h at 20 °C, then the brood size was counted. (B)The body sizes were determined by measuring the flat surface areaof the worms using ImageJ software, and there was no difference amongall treatments after L1-stage larvae were treated with DPE and/orUVA for 72 h. (C) Life span curves of worms and (D) the percentageof adult worms were scored after L1-stage larvae were treated withDPE and/or UVA for 72 h. Data were pooled from three independent experiments.All values are presented as the means ± SE; n ≥ 20, and * represents P < 0.05.

Mentions:
Environmental stresses could modify the developmentalprocesses when the larvae were exposed to toxicants either in embryonicdevelopment or early developmental stages.39 In C. elegans, germ cell apoptosis commences inearly adulthood and increases over time.24 To exclude the changes of background value, we investigated thedevelopmental effects by DPE plus UVA at different stages. As shownin Figure 2B and Figure 5A, worms coexposed to DPE plus UVA at the L4 stage had little effecton the index of mitotic germ cells and brood size. In addition, thebody size and the life span of worms exposed to DPE plus UVA at theL1 stage were not changed obviously as well (Figure 5B and C). However, there was a slight decrease in the percentageof adult worms compared to that in the single treatment of DPE orUVA, or to the control (in all cases, P > 0.05)whenworms were coexposed to DPE plus UVA at the L1 stage (Figure 5D). The results indicated that the enhanced levelsof germ cell apoptosis after coexposure to DPE plus UVA at the latestage did not result from the modification of the developmental procedure.

Bottom Line:
Diesel exhaust has been classified as a potential carcinogen and is associated with various health effects.A previous study showed that the doses for manifesting the mutagenetic effects of diesel exhaust could be reduced when coexposed with ultraviolet-A (UVA) in a cellular system.Our results demonstrated that though coexposure of wild type worms at young adult stage to low doses of DPE (20 μg/mL) plus UVA (0.2, 0.5, and 1.0 J/cm2) did not affect worm development (mitotic germ cells and brood size), it resulted in a significant induction of germ cell death.

ABSTRACTDiesel exhaust has been classified as a potential carcinogen and is associated with various health effects. A previous study showed that the doses for manifesting the mutagenetic effects of diesel exhaust could be reduced when coexposed with ultraviolet-A (UVA) in a cellular system. However, the mechanisms underlying synergistic effects remain to be clarified, especially in an in vivo system. In the present study, using Caenorhabditis elegans (C. elegans) as an in vivo system we studied the synergistic effects of diesel particulate extract (DPE) plus UVA, and the underlying mechanisms were dissected genetically using related mutants. Our results demonstrated that though coexposure of wild type worms at young adult stage to low doses of DPE (20 μg/mL) plus UVA (0.2, 0.5, and 1.0 J/cm2) did not affect worm development (mitotic germ cells and brood size), it resulted in a significant induction of germ cell death. Using the strain of hus-1::gfp, distinct foci of HUS-1::GFP was observed in proliferating germ cells, indicating the DNA damage after worms were treated with DPE plus UVA. Moreover, the induction of germ cell death by DPE plus UVA was alleviated in single-gene loss-of-function mutations of core apoptotic, checkpoint HUS-1, CEP-1/p53, and MAPK dependent signaling pathways. Using a reactive oxygen species (ROS) probe, it was found that the production of ROS in worms coexposed to DPE plus UVA increased in a time-dependent manner. In addition, employing a singlet oxygen (1O2) trapping probe, 2,2,6,6-tetramethyl-4-piperidone, coupled with electron spin resonance analysis, we demonstrated the increased 1O2 production in worms coexposed to DPE plus UVA. These results indicated that UVA could enhance the apoptotic induction of DPE at low doses through a DNA damage-triggered pathway and that the production of ROS, especially (1)O2, played a pivotal role in initiating the synergistic process.